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A triangle is formed by the joining the points (0, 0), (0, 15) and (18, 0). How many points having integral coordinates lie strictly inside the triangle?
  • a)
    124
  • b)
    138
  • c)
    134
  • d)
    None of these
Correct answer is option 'D'. Can you explain this answer?
Verified Answer
A triangle is formed by the joining the points (0, 0), (0, 15) and (18...
Solution: The three points form a right angled triangle. The equation of its hypotenuse by intercept form is  
Consider a rectangle whose vertices are (0, 0), (0,15), (18, 0) and (18,15). 1 4 x 17 = 238 points are strictly inside the rectangle. Let P point lie on the hypotenuse 5x + 6 y = 90. Half of (238 - P) points will lie on either sides of the hypotenuse.
So the required number must be less than 119. Hence, option 4.
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Most Upvoted Answer
A triangle is formed by the joining the points (0, 0), (0, 15) and (18...
To find the number of points with integral coordinates that lie strictly inside the triangle, we can use the Pick's Theorem.

Pick's Theorem states that for a polygon on a grid with vertices having integral coordinates, the number of points with integral coordinates strictly inside the polygon (denoted as I) can be calculated using the formula:

I = A - B/2 + 1

where A represents the number of points with integral coordinates on the boundary of the polygon, and B represents the number of points with integral coordinates in the interior of the polygon.

To apply Pick's Theorem to the given triangle, we need to calculate A and B.

1. Calculating A (number of boundary points with integral coordinates):

The given triangle has three sides:
- Side 1: (0, 0) to (0, 15)
- Side 2: (0, 15) to (18, 0)
- Side 3: (18, 0) to (0, 0)

The length of side 1 is 15, so there are 15 points with integral coordinates on this side.
The length of side 2 is 18, so there are 18 points with integral coordinates on this side.
The length of side 3 is also 18, so there are 18 points with integral coordinates on this side.

Therefore, the total number of boundary points with integral coordinates (A) is 15 + 18 + 18 = 51.

2. Calculating B (number of interior points with integral coordinates):

To calculate the number of interior points with integral coordinates (B), we can use the Shoelace Formula.

The Shoelace Formula for a triangle with vertices (x1, y1), (x2, y2), and (x3, y3) is given by:

B = (|x1y2 + x2y3 + x3y1 - y1x2 - y2x3 - y3x1| - 2) / 2

Applying the coordinates of the given triangle, we have:

B = (|0*15 + 0*0 + 18*0 - 0*0 - 15*18 - 0*0| - 2) / 2
= (|-270| - 2) / 2
= (270 - 2) / 2
= 268 / 2
= 134

Therefore, the number of interior points with integral coordinates (B) is 134.

3. Calculating I (number of interior points strictly inside the triangle):

Using Pick's Theorem:

I = A - B/2 + 1
= 51 - 134/2 + 1
= 51 - 67 + 1
= -15

Since the number of interior points strictly inside the triangle (I) is -15, which is not a valid answer, the correct option is D - None of these.

Hence, there are no points with integral coordinates strictly inside the given triangle.
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